1. Field of the Invention
The present inventions relates generally to motorcycles and, more particularly, to motorcycle steering mechanisms. Specifically, the present invention relates to an improved motorocycle steering mechanism which permits continuous automatic adjustment of the rake or fork angle of the motorcycle's front wheel during operation thereof.
2. Description of the Prior Art
The steering and stability characteristics of motorcycles, bicycles and other similar types of vehicles can be varied and altered in a number of different ways. One particular design aspect which is important to the steering and stability characteristics of a motorcycle involves the rake and fork angles of the front wheel assembly. The rake angle is defined as that angle which the steering axis of the front wheel assembly of the motorcycle has relative to an imaginary vertical axis or plane. Thus, if an imaginary vertical plane is passed through the steering head assembly of a motorcycle, the rake angle is that angle formed between such plane and the steering axis of the front wheel assembly. The fork angle is defined as the angle which the axis of the front fork assembly has relative to the aforesaid vertical axis or plane. Depending on the design of the motorcycle, the rake and fork angles may or may not be identical. If the steering axis is coaxial with the front fork assembly axis, then the rake and fork angles are always identical. In some motorcycle designs, however, the steering axis is set rearwardly along the motorcycle relative to the front fork assembly axis. In this instance, the rake and fork angles are separate and may therefore by set differently from each other.
Variations in the rake or fork angle of a motorcycle will provide different ride and steering characteristics. In fact, these angles are quite critical to the handling of racing as well as off-road types of motorcycles. Assuming for the moment that the rake and fork angles are identical, if the fork angle is large, such as 35.degree. or so, the motorcycle generally tends to be very stable at high speeds on a straight course but is difficult to steer through bends. On the other hand, if the fork angle is considerably smaller, i.e., approximately 25.degree. or less, the motorcycle steering will be quite sensitive and responsive, but the stability of the motorcycle on a fast straight section of road tends to be considerably less than desirable. Thus, an optimum design for off-road "dirt" motorcycles is to have as small a fork angle as possible, since stability along straight, flat pavement sections is not a significant factor. Likewise, an optimum design for a racing motorcycle for long, straight raceways includes as large a fork angle as possible while providing acceptable steering characteristics as well.
Heretofore, most motorcycle designs have represented a compromise by choosing a fork angle somewhere between the above extremes to achieve acceptable stability as well as turning characteristics. However, certain motorcycle designs have been devised which allow changing of the fork angle depending upon road conditions and motorcycle use. In particular, U.S. Pat. Nos. 3,866,946 and 4,082,307, U.K. Pat. No. 570,439 and Italian Pat. No. 523,424 all disclose various mechanical arrangements which permit the rake or fork angle of the front fork assembly of a motorcycle to be changed. While each of the designs disclosed in these particular patents are specifically different, they all achieve fork angle change basically in the same manner. This manner requires that the motorcycle be stopped, that the operator then disassemble portions of the motorcycle steering head assembly to remove or alter components thereof in order to change the fork angle, and that the operator then reassemble the steering head components with the fork angle at its new position. Should the operator subsequently choose to again change the fork angle due to new road conditions or the like, the same cumbersome and time consuming procedure is required. Thus, while the fork angle of such motorcycle steering mechanism designs is variable, it certainly is not automatically variable nor can it be varied conveniently. Moreover, these designs do not permit variance of the fork angle during actual operation of the motorcycle.
U.S. Pat. No. 4,378,857 discloses another type of steering mechanism design which does permit variance of the fork angle during operation of the motorcycle. In this particular design, the steering head assembly is freely, pivotally movable along the longitudinal axis of the motorcycle and is connected to the rear drive wheel of the motorcycle by a shock absorber mechanism. In this manner, the fork angle will automatically vary during the course of operation of the motorcycle depending upon the acceleration or deceleration of the motorcycle, the roughness of the road terrain and the like. In other words, as the rear wheel of the motorcycle of this particular design bounces vertically or moves longitudinally relative to the front wheel, e.g. during rapid acceleration or deceleration, the fork angle will automatically change. Thus, the variability of the fork angle in this design is dependent entirely on operating and road conditions and in many instances is not under the control of the motorcycle operator. Consequently, there is still a need for a motorcycle steering mechanism design wherein the fork angle can be easily changed as desired by the motorcycle operator to permit larger fork angle adjustments during straight away motorcycle operation and shorter fork angle adjustments during turning and off-road operations.